1. Field of the Invention
The present invention relates to star-shaped polymers with a plurality of poly(hydroxyacid) branches or arms attached to a central polyfunctional compound at branching locations that were originally a plurality of hydroxyl or amino groups. More specifically but not by way of limitation, the invention relates to star-shaped polymers having a central sugar or sugar related residue with sequential amorphous polymer blocks followed by semicrystalline homopolymer blocks of polylactide, polyglycolide, polycaprolactone, or the like.
2. Description of the Related Art
Saotome and Kodatra in "Polymerization of delta-Valerolac-tone and Preparation of a Thermostable Derivative from a Polyester", Macromol. Chem., 82 pp. 41-52 (1964) describe the polymerization of delta-valerolactone using initiators which have active hydrogen atoms in their molecule, such as ethylene glycol or ethanol amine. The polymers produced with these initiators have hydroxyl groups at both ends of the polymer chain.
Zhu et al. in "Preparation, Characterization, and Properties of Polylactide (PLA)-Poly (Ethylene Glycol) (PEG) Copolymers: A Potential Drug Carrier", Journal of Applied Polymer Science, Vol 39, pages 1-9 (1990) describe the use of oligomeric and polymeric polyethylene with hydroxyl end groups for polymerization of lactide.
Zhu et al. "Super Microcapsules (SMC). I. Preparation and Characterization of Star Polyethylene Oxide (PEO)-Polylactide (PLA) Copolymers.", Journal of Polymer Science: Part A: Polymer Chemistry, Vol 27, pages 2151-2159 (1989) describe polymerization of lactide from 3-arm and 4-arm hydrophilic poly (ethylene oxide) with hydroxylterminated arms.